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From "Stefan Egli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-8351) Long running RGC remove and getmore operations
Date Wed, 26 Jun 2019 13:53:00 GMT

    [ https://issues.apache.org/jira/browse/OAK-8351?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16873346#comment-16873346
] 

Stefan Egli commented on OAK-8351:
----------------------------------

backport to 1.8 ready in appropriate svn merge format :  [^OAK-8351-merged-1.8.patch] 

> Long running RGC remove and getmore operations
> ----------------------------------------------
>
>                 Key: OAK-8351
>                 URL: https://issues.apache.org/jira/browse/OAK-8351
>             Project: Jackrabbit Oak
>          Issue Type: Bug
>          Components: mongomk
>    Affects Versions: 1.12.0
>            Reporter: Stefan Egli
>            Assignee: Stefan Egli
>            Priority: Major
>              Labels: candidate_oak_1_8
>             Fix For: 1.10.3, 1.16.0
>
>         Attachments: OAK-8351-1.10.patch, OAK-8351-1.8.patch, OAK-8351-merged-1.8.patch,
OAK-8351.patch
>
>
> On a mongodb setup a long running revision garbage collection operation has been witnessed.
The query was running for hours. Doing a {{planCacheSetFilter}}, which hinted mongodb to use
a specific index, together with killing the running command resolved the situation.
> The problem was that mongodb generated a query plan which scored high (2.0003) but included
an index scan through the {{\_id_}} index (and the collection contained millions of documents).
It also generated other, better, plans, but they all "only" had the same high score, so it
seemed legitimate that mongodb would choose this one.
> The reason why this, problematic, query plan resulted in a high score seems to be that
it does indeed find 101 documents after entering the first "or" - but during query execution
it would also enter the other "or" parts where it has chosen to do a {{\_id_}} index scan.
> The query involved was:
> {noformat}
> 					{
> 						"_sdType" : {
> 								"$in" : [
> 										50,
> 										60,
> 										70
> 								]
> 						},
> 						"$or" : [
> 								{
> 										"_sdType" : 50
> 								},
> 								{
> 										"_sdType" : 60
> 								},
> 								{
> 										"_sdType" : 70,
> 										"$or" : [
> 												{
> 														"_id" : /.*-1\/0/
> 												},
> 												{
> 														"_id" : /[^-]*/,
> 														"_path" : /.*-1\/0/
> 												}
> 										],
> 										"_sdMaxRevTime" : {
> 												"$lt" : NumberLong(1551843365)
> 										}
> 								},
> 								{
> 										"_sdType" : 70,
> 										"$or" : [
> 												{
> 														"_id" : /.*-2\/0/
> 												},
> 												{
> 														"_id" : /[^-]*/,
> 														"_path" : /.*-2\/0/
> 												}
> 										],
> 										"_sdMaxRevTime" : {
> 												"$lt" : NumberLong(1550757370)
> 										}
> 								}
> 						],
> 						"_sdMaxRevTime" : {
> 								"$lt" : NumberLong(1551756965)
> 						}
> 				}
> {noformat}
> The problematic plan was:
> {noformat}
> 	{
> 			"details" : {
> 				"solution" : "(index-tagged expression tree: tree=Node\n---Node\n------Node\n---------Node\n------------Node\n---------------Leaf
_id_, pos: 0, can combine? 1\n---------------Leaf \n------------Leaf _id_, pos: 0, can combine?
1\n---------Leaf \n---------Leaf \n------Node\n---------Node\n------------Node\n---------------Leaf
_id_, pos: 0, can combine? 1\n---------------Leaf \n------------Leaf _id_, pos: 0, can combine?
1\n---------Leaf \n---------Leaf \n------Leaf _sdType_1__sdMaxRevTime_1, pos: 0, can combine?
1\n------Leaf _sdType_1__sdMaxRevTime_1, pos: 0, can combine? 1\n---Leaf Move to 2: _sdType_1__sdMaxRevTime_1,
pos: 1, can combine? 1. Move to 3: _sdType_1__sdMaxRevTime_1, pos: 1, can combine? 1. \n---Leaf
Move to 2: _sdType_1__sdMaxRevTime_1, pos: 0, can combine? 1. Move to 3: _sdType_1__sdMaxRevTime_1,
pos: 0, can combine? 1. \n)"
> 			},
> 			"reason" : {
> 				"score" : 2.0003,
> 				"stats" : {
> 					"stage" : "FETCH",
> 					"filter" : {
> 						"$and" : [
> 							{
> 								"_sdMaxRevTime" : {
> 									"$lt" : NumberLong(1551410180)
> 								}
> 							},
> 							{
> 								"_sdType" : {
> 									"$in" : [
> 										50,
> 										60,
> 										70
> 									]
> 								}
> 							}
> 						]
> 					},
> 					"nReturned" : 101,
> 					"executionTimeMillisEstimate" : 0,
> 					"works" : 101,
> 					"advanced" : 101,
> 					"needTime" : 0,
> 					"needYield" : 0,
> 					"saveState" : 3,
> 					"restoreState" : 3,
> 					"isEOF" : 0,
> 					"invalidates" : 0,
> 					"docsExamined" : 101,
> 					"alreadyHasObj" : 0,
> 					"inputStage" : {
> 						"stage" : "OR",
> 						"nReturned" : 101,
> 						"executionTimeMillisEstimate" : 0,
> 						"works" : 101,
> 						"advanced" : 101,
> 						"needTime" : 0,
> 						"needYield" : 0,
> 						"saveState" : 3,
> 						"restoreState" : 3,
> 						"isEOF" : 0,
> 						"invalidates" : 0,
> 						"dupsTested" : 101,
> 						"dupsDropped" : 0,
> 						"recordIdsForgotten" : 0,
> 						"inputStages" : [
> 							{
> 								"stage" : "IXSCAN",
> 								"nReturned" : 101,
> 								"executionTimeMillisEstimate" : 0,
> 								"works" : 101,
> 								"advanced" : 101,
> 								"needTime" : 0,
> 								"needYield" : 0,
> 								"saveState" : 3,
> 								"restoreState" : 3,
> 								"isEOF" : 0,
> 								"invalidates" : 0,
> 								"keyPattern" : {
> 									"_sdType" : 1,
> 									"_sdMaxRevTime" : 1
> 								},
> 								"indexName" : "_sdType_1__sdMaxRevTime_1",
> 								"isMultiKey" : false,
> 								"multiKeyPaths" : {
> 									"_sdType" : [ ],
> 									"_sdMaxRevTime" : [ ]
> 								},
> 								"isUnique" : false,
> 								"isSparse" : true,
> 								"isPartial" : false,
> 								"indexVersion" : 2,
> 								"direction" : "forward",
> 								"indexBounds" : {
> 									"_sdType" : [
> 										"[50, 50]"
> 									],
> 									"_sdMaxRevTime" : [
> 										"[-inf.0, 1551410180)"
> 									]
> 								},
> 								"keysExamined" : 101,
> 								"seeks" : 1,
> 								"dupsTested" : 0,
> 								"dupsDropped" : 0,
> 								"seenInvalidated" : 0
> 							},
> 							{
> 								"stage" : "IXSCAN",
> 								"nReturned" : 0,
> 								"executionTimeMillisEstimate" : 0,
> 								"works" : 0,
> 								"advanced" : 0,
> 								"needTime" : 0,
> 								"needYield" : 0,
> 								"saveState" : 3,
> 								"restoreState" : 3,
> 								"isEOF" : 0,
> 								"invalidates" : 0,
> 								"keyPattern" : {
> 									"_sdType" : 1,
> 									"_sdMaxRevTime" : 1
> 								},
> 								"indexName" : "_sdType_1__sdMaxRevTime_1",
> 								"isMultiKey" : false,
> 								"multiKeyPaths" : {
> 									"_sdType" : [ ],
> 									"_sdMaxRevTime" : [ ]
> 								},
> 								"isUnique" : false,
> 								"isSparse" : true,
> 								"isPartial" : false,
> 								"indexVersion" : 2,
> 								"direction" : "forward",
> 								"indexBounds" : {
> 									"_sdType" : [
> 										"[60, 60]"
> 									],
> 									"_sdMaxRevTime" : [
> 										"[-inf.0, 1551410180)"
> 									]
> 								},
> 								"keysExamined" : 0,
> 								"seeks" : 0,
> 								"dupsTested" : 0,
> 								"dupsDropped" : 0,
> 								"seenInvalidated" : 0
> 							},
> 							{
> 								"stage" : "FETCH",
> 								"filter" : {
> 									"$and" : [
> 										{
> 											"_sdType" : {
> 												"$eq" : 70
> 											}
> 										},
> 										{
> 											"_sdMaxRevTime" : {
> 												"$lt" : NumberLong(1551496575)
> 											}
> 										}
> 									]
> 								},
> 								"nReturned" : 0,
> 								"executionTimeMillisEstimate" : 0,
> 								"works" : 0,
> 								"advanced" : 0,
> 								"needTime" : 0,
> 								"needYield" : 0,
> 								"saveState" : 3,
> 								"restoreState" : 3,
> 								"isEOF" : 0,
> 								"invalidates" : 0,
> 								"docsExamined" : 0,
> 								"alreadyHasObj" : 0,
> 								"inputStage" : {
> 									"stage" : "OR",
> 									"nReturned" : 0,
> 									"executionTimeMillisEstimate" : 0,
> 									"works" : 0,
> 									"advanced" : 0,
> 									"needTime" : 0,
> 									"needYield" : 0,
> 									"saveState" : 3,
> 									"restoreState" : 3,
> 									"isEOF" : 0,
> 									"invalidates" : 0,
> 									"dupsTested" : 0,
> 									"dupsDropped" : 0,
> 									"recordIdsForgotten" : 0,
> 									"inputStages" : [
> 										{
> 											"stage" : "FETCH",
> 											"filter" : {
> 												"_path" : {
> 													"$regex" : ".*-1/0"
> 												}
> 											},
> 											"nReturned" : 0,
> 											"executionTimeMillisEstimate" : 0,
> 											"works" : 0,
> 											"advanced" : 0,
> 											"needTime" : 0,
> 											"needYield" : 0,
> 											"saveState" : 3,
> 											"restoreState" : 3,
> 											"isEOF" : 0,
> 											"invalidates" : 0,
> 											"docsExamined" : 0,
> 											"alreadyHasObj" : 0,
> 											"inputStage" : {
> 												"stage" : "IXSCAN",
> 												"filter" : {
> 													"_id" : {
> 														"$regex" : "[^-]*"
> 													}
> 												},
> 												"nReturned" : 0,
> 												"executionTimeMillisEstimate" : 0,
> 												"works" : 0,
> 												"advanced" : 0,
> 												"needTime" : 0,
> 												"needYield" : 0,
> 												"saveState" : 3,
> 												"restoreState" : 3,
> 												"isEOF" : 0,
> 												"invalidates" : 0,
> 												"keyPattern" : {
> 													"_id" : 1
> 												},
> 												"indexName" : "_id_",
> 												"isMultiKey" : false,
> 												"multiKeyPaths" : {
> 													"_id" : [ ]
> 												},
> 												"isUnique" : true,
> 												"isSparse" : false,
> 												"isPartial" : false,
> 												"indexVersion" : 2,
> 												"direction" : "forward",
> 												"indexBounds" : {
> 													"_id" : [
> 														"[\"\", {})",
> 														"[/[^-]*/, /[^-]*/]"
> 													]
> 												},
> 												"keysExamined" : 0,
> 												"seeks" : 0,
> 												"dupsTested" : 0,
> 												"dupsDropped" : 0,
> 												"seenInvalidated" : 0
> 											}
> 										},
> 										{
> 											"stage" : "IXSCAN",
> 											"filter" : {
> 												"$or" : [
> 													{
> 														"_id" : {
> 															"$regex" : ".*-1/0"
> 														}
> 													}
> 												]
> 											},
> 											"nReturned" : 0,
> 											"executionTimeMillisEstimate" : 0,
> 											"works" : 0,
> 											"advanced" : 0,
> 											"needTime" : 0,
> 											"needYield" : 0,
> 											"saveState" : 3,
> 											"restoreState" : 3,
> 											"isEOF" : 0,
> 											"invalidates" : 0,
> 											"keyPattern" : {
> 												"_id" : 1
> 											},
> 											"indexName" : "_id_",
> 											"isMultiKey" : false,
> 											"multiKeyPaths" : {
> 												"_id" : [ ]
> 											},
> 											"isUnique" : true,
> 											"isSparse" : false,
> 											"isPartial" : false,
> 											"indexVersion" : 2,
> 											"direction" : "forward",
> 											"indexBounds" : {
> 												"_id" : [
> 													"[\"\", {})",
> 													"[/.*-1/0/, /.*-1/0/]"
> 												]
> 											},
> 											"keysExamined" : 0,
> 											"seeks" : 0,
> 											"dupsTested" : 0,
> 											"dupsDropped" : 0,
> 											"seenInvalidated" : 0
> 										}
> 									]
> 								}
> 							},
> 							{
> 								"stage" : "FETCH",
> 								"filter" : {
> 									"$and" : [
> 										{
> 											"_sdType" : {
> 												"$eq" : 70
> 											}
> 										},
> 										{
> 											"_sdMaxRevTime" : {
> 												"$lt" : NumberLong(1550757370)
> 											}
> 										}
> 									]
> 								},
> 								"nReturned" : 0,
> 								"executionTimeMillisEstimate" : 0,
> 								"works" : 0,
> 								"advanced" : 0,
> 								"needTime" : 0,
> 								"needYield" : 0,
> 								"saveState" : 3,
> 								"restoreState" : 3,
> 								"isEOF" : 0,
> 								"invalidates" : 0,
> 								"docsExamined" : 0,
> 								"alreadyHasObj" : 0,
> 								"inputStage" : {
> 									"stage" : "OR",
> 									"nReturned" : 0,
> 									"executionTimeMillisEstimate" : 0,
> 									"works" : 0,
> 									"advanced" : 0,
> 									"needTime" : 0,
> 									"needYield" : 0,
> 									"saveState" : 3,
> 									"restoreState" : 3,
> 									"isEOF" : 0,
> 									"invalidates" : 0,
> 									"dupsTested" : 0,
> 									"dupsDropped" : 0,
> 									"recordIdsForgotten" : 0,
> 									"inputStages" : [
> 										{
> 											"stage" : "FETCH",
> 											"filter" : {
> 												"_path" : {
> 													"$regex" : ".*-2/0"
> 												}
> 											},
> 											"nReturned" : 0,
> 											"executionTimeMillisEstimate" : 0,
> 											"works" : 0,
> 											"advanced" : 0,
> 											"needTime" : 0,
> 											"needYield" : 0,
> 											"saveState" : 3,
> 											"restoreState" : 3,
> 											"isEOF" : 0,
> 											"invalidates" : 0,
> 											"docsExamined" : 0,
> 											"alreadyHasObj" : 0,
> 											"inputStage" : {
> 												"stage" : "IXSCAN",
> 												"filter" : {
> 													"_id" : {
> 														"$regex" : "[^-]*"
> 													}
> 												},
> 												"nReturned" : 0,
> 												"executionTimeMillisEstimate" : 0,
> 												"works" : 0,
> 												"advanced" : 0,
> 												"needTime" : 0,
> 												"needYield" : 0,
> 												"saveState" : 3,
> 												"restoreState" : 3,
> 												"isEOF" : 0,
> 												"invalidates" : 0,
> 												"keyPattern" : {
> 													"_id" : 1
> 												},
> 												"indexName" : "_id_",
> 												"isMultiKey" : false,
> 												"multiKeyPaths" : {
> 													"_id" : [ ]
> 												},
> 												"isUnique" : true,
> 												"isSparse" : false,
> 												"isPartial" : false,
> 												"indexVersion" : 2,
> 												"direction" : "forward",
> 												"indexBounds" : {
> 													"_id" : [
> 														"[\"\", {})",
> 														"[/[^-]*/, /[^-]*/]"
> 													]
> 												},
> 												"keysExamined" : 0,
> 												"seeks" : 0,
> 												"dupsTested" : 0,
> 												"dupsDropped" : 0,
> 												"seenInvalidated" : 0
> 											}
> 										},
> 										{
> 											"stage" : "IXSCAN",
> 											"filter" : {
> 												"$or" : [
> 													{
> 														"_id" : {
> 															"$regex" : ".*-2/0"
> 														}
> 													}
> 												]
> 											},
> 											"nReturned" : 0,
> 											"executionTimeMillisEstimate" : 0,
> 											"works" : 0,
> 											"advanced" : 0,
> 											"needTime" : 0,
> 											"needYield" : 0,
> 											"saveState" : 3,
> 											"restoreState" : 3,
> 											"isEOF" : 0,
> 											"invalidates" : 0,
> 											"keyPattern" : {
> 												"_id" : 1
> 											},
> 											"indexName" : "_id_",
> 											"isMultiKey" : false,
> 											"multiKeyPaths" : {
> 												"_id" : [ ]
> 											},
> 											"isUnique" : true,
> 											"isSparse" : false,
> 											"isPartial" : false,
> 											"indexVersion" : 2,
> 											"direction" : "forward",
> 											"indexBounds" : {
> 												"_id" : [
> 													"[\"\", {})",
> 													"[/.*-2/0/, /.*-2/0/]"
> 												]
> 											},
> 											"keysExamined" : 0,
> 											"seeks" : 0,
> 											"dupsTested" : 0,
> 											"dupsDropped" : 0,
> 											"seenInvalidated" : 0
> 										}
> 									]
> 								}
> 							}
> 						]
> 					}
> 				}
> 			},
> 			"feedback" : {
> 				"nfeedback" : 18,
> 				"scores" : [
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					},
> 					{
> 						"score" : 2.0003
> 					}
> 				]
> 			},
> 			"filterSet" : false
> 		}
> {noformat}



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